1. Field of the Invention
This invention relates to a two-way optical transmitter, and particularly to a two-way optical transmitter which utilizes linearly polarized light of a modulated light signal, for example, with space as a transmission medium and which is good in transmission efficiency and can accomplish transmission with high accuracy and good operability.
2. Related Background Art
There have heretofore been proposed various two-way optical transmitters designed to effect the transmission and reception of light signals with space as a transmission medium.
FIG. 5A of the accompanying drawings is a schematic view of the essential portions of the optical system of a two-way optical transmitter according to the prior art utilizing polarized light. In FIG. 5A, the reference numerals 16 and 17 designate a pair of left and right optical transmitters comprising the same construction and disposed in opposed relationship with each other with a predetermined distance interposed therebetween. The right optical transmitter 17 is disposed in such a positional relation that the left optical transmitter 16 has been rotated by 90.degree. about the X-axis which is the direction of optical transmission. FIG. 5B of the accompanying drawings is a plan (X-Z plane) view of the optical transmitter 17.
Description will now be made of a case where a light signal is transmitted from the left optical transmitter 16 to the right optical transmitter 17.
A linearly polarized laser beam La emitted from a laser diode 1a has its direction of polarization coinciding with the direction of the Z-axis as indicated by arrow 19. The laser beam La passes through a lens unit 2a having positive power and becomes a substantially parallel light beam and enters the cemented surface 3aa (obliquely disposed at an angle of 45.degree. with respect to the X-Z plane) of a polarizing beam splitter 3a. Almost all of the laser beam La which has entered the cemented surface 3aa is reflected and enters a beam expander 101a having a lens 14a and a lens 15a.
The laser beam La which has entered the beam expander 101a has its beam diameter enlarged and emerges as linearly polarized light having a plane of polarization in the direction of the Z-axis (the direction of arrow 19) from the beam expander 101a.
That is, the laser beam La emerges from the optical transmitter 16 and enters the right optical transmitter 17. The laser beam La which has entered the right optical transmitter 17 passes through a beam expander 101b, whereafter it enters a polarizing beam splitter 3b.
Almost all of the linearly polarized laser beam La having its plane of polarization in the direction of the Z-axis which has entered the polarizing beam splitter 3b passes through the cemented surface (obliquely disposed at an angle of 45.degree. with respect to the X-Y plane) of the polarizing beam splitter 3b and is condensed on a light receiving element 5b by a lens unit 4b having positive power. Thereby the light signal is received.
What has been described above also holds true when a light signal is transmitted from the right optical transmitter 17 to the left optical transmitter 16.
That is, a laser beam Lb from a laser diode 1b has its direction of polarization coinciding with the direction of the Y-axis as indicated by arrow 21. Almost all of this linearly polarized laser beam Lb is reflected by the cemented surface 3bb of a polarizing beam splitter 3b and enters the left optical transmitter 16 through the beam expander 101b.
Almost all of the laser beam Lb which has entered the optical transmitter 16 passes through the beam expander 101a and through the cemented surface 3aa of the polarizing beam splitter 3a, and is condensed on a light receiving element 5a by a lens unit 4a having positive power. In FIGS. 5A and 5B, the two-way transmission of the light signal is effected by such a construction.
In the prior-art two-way optical transmitter shown in FIGS. 5A and 5B, two kinds of optical transmitters differing in the arrangement and structure of elements (parts) from each other are disposed in opposed relationship with each other to thereby effect two-way optical transmission. Therefore, to utilize these optical transmitters, the distinction of the combination of the optical transmitters and the distinction of the handling thereof are required. This has led to the problem that confusion in operation results.